Because of their thermal and oxidative stability and wide fluid ranges perfluoroalkylether fluids are being considered for use as engine oils, hydraulic fluids and greases and are actually used currently in space guidance systems. However, in oxidizing atmospheres and under conditions of boundary lubrications these compositions corrode metals/metal alloys and provide volatile degradation products. Two kinds of additives were found to be effective in arresting the degradation process namely phospha-s-triazines described by K. L. Paciorek, R. H. Kratzer, J. Kaufman and T. I. Ito in U.S. Pat. No. 4,215,072 (1980), and by K. L. Paciorek, R. H. Kratzer, J. Kaufman and T. I. Ito in U.S. Pat. No. 4,166,071 (1979). The other type of additives are the phosphines described by C. E. Snyder, Jr. and C. Tamborski in U.S. Pat. No. 4,097,388 (1978) and C. T. Tamborski, C. E. Snyder, Jr. and J. B. Christian in U.S. Pat. No. 4,454,349 (1984). Both types of the additives exhibit some shortcomings the phospha-s-triazines are susceptible to hydrolysis whereas the phosphines exhibit limited thermal oxidative stability. This invention pertains specifically to the synthesis of hindered monophospha-s-triazines which exhibit high hydrolytic stability, as compared to previously synthesized analogues, without a decrease in their inhibition of metal corrosion and fluid degradation. These monophospha-s-triazines and the chemical intermediates employed in their preparation and disclosed herein are, to the best of our knowledge, new chemical compounds previously unknown.